The Relationship between Rhizobacteria Auxin Production and Wheat Biomass Productivity is Negative

Abstract

ABSTRACT Auxin, a plant growth-promoting hormone, is known to be produced by many if not all bacteria. Research has shown that bacteria produced auxin is associated with both positive and negative plant growth effects. Here we determined the relationship between auxin production capacity and wheat biomass productivity in culturally isolated bacteria. A total of 4320 individual bacteria were isolated and characterized based on colony size as either fast (>2 mm) or slow (<2 mm) growing, from the rhizospheres and endorhizospheres of wheat plants grown in two soils that differ in pH and texture. The bacteria were assayed for auxin production based on a Salkowski reagent microplate assay. The relationship between auxin production and wheat biomass was largely negative under all conditions and characterizations, and non-significant (R2 0.04 to 0.26). When examined across all treatments, the lowest auxin producers originated from the highest biomass plants and the highest auxin producers from the lowest biomass plants (p value < .0001). Fast growing colonies produced significantly higher auxin production than slow growing colonies, overall (p value ≤ 0.005). The results suggest that auxin production by culturally isolated bacteria, as determined by the Salkowski reagent, is negatively associated with wheat biomass productivity.